The present invention relates to a charging plate for liquid jet charging devices wherein a liquid filament injected through an orifice provided on an orifice member is electrostatically charged so that charged liquid droplets are formed by mechanically subdividing the liquid filament, and a method for making the same.
This type of charging plate having a construction where a plurality of electrodes are arranged in parallel and printed on a side surface of a substrate of the charging plate is well known. Current-carrying parts for electrically connecting each of the electrodes are printed on the upper surface of the substrate.
FIG. 8 is a cross-sectional side view of assistance in explaining the construction of a liquid jet charging device having a charging plate of the conventional type (hereinafter referred to the prior art.). In the figure, 1C denotes a charging plate for the device. The charging plate 1C has such a construction that a plurality of electrodes 4 made of electrically conductive substance are arranged on one side surface 3 of a substrate 2 made of non-conductive substance, such as ceramics, at almost equal intervals in the depth direction (into the page in the figure) of the side surface 3, and current-carrying parts 5 made of conductive substance are provided on an upper surface 7 of the substrate 2 as extending from the electrodes 4 individually.
Next, numeral 21 denotes an orifice member on the lower part of which an orifice 22 is provided.
The liquid jet charging device having the charging plate 1C of the conventional type is operated in the following manner.
The pressurized liquid is continuously injected as a liquid filament 23 through an orifice on a high-frequency oscillated orifice member 21. Liquid droplets 24 and 24xe2x80x2 are generated and flown one after another as the liquid filament 23 is forcibly subdivided from the tip of the liquid filament 23 in accordance with the frequency of the high-frequency oscillation.
When a liquid inside the orifice member 21 is appropriately pressurized and vibrated at an appropriate frequency to obtain the droplets 24 and 24xe2x80x2 in a stable state, the liquid filament 23, whose length a is not more than 1 millimeter, is divided into droplets 24 and 24xe2x80x2 beyond the tip thereof and flies in the air.
To cause the droplets 24 and 24xe2x80x2 to be produced in an adequately charged state as the liquid filament 23 is subdivided, it is known that the electrode 4 be disposed as near as a few micrometers to ten-odd micrometers by the side of the liquid filament 23, and in front and rear of a location where the liquid filament 23 is subdivided into the droplets 24 and 24xe2x80x2 beyond the tip thereof.
Furthermore, it is also known that as a DC voltage is applied to the electrode 4 for a very short time in synchronism with the timing at which the liquid filament 23 is subdivided into droplets 24 and 24xe2x80x2 from the tip thereof, an electric charge is induced for that very short time in the liquid filament corresponding to the electrode 4, and as a result, the droplets 24 and 24xe2x80x2 divided from the liquid filament 23 travel in the air in a charged state.
The conventional type of charging plate 1C shown in FIG. 8, on the other hand, is given in advance appropriate roundness on the upper and lower edges 101 and 102 of one side surface 3 of the substrate 2 made of non-conductive material, as shown in the figure. An electrically conductive film is formed over an area ranging from the side surface 3 to the upper surface 7 of the substrate 2, and then a plurality of electrodes 4 are formed on the side surface 3 of the substrate 2 and the current-carrying portions 5 extending from the electrodes 4 are formed on the upper surface 7 of the substrate by removing the conductive film from parts other than the desired electrodes 4 and current-carrying portions 5.
The charging plate 1C is given in advance appropriate roundness on the upper and lower edges 101 and 102 consisting of the upper surface 7, the lower surface 6 and the side surface 3 of the substrate 2 for a machining convenience, with the radii of the roundness at the upper and lower edges being 0.5 millimeters to 1 millimeter.
Forming roundness on one edge of both the edges 101 and 102 has been particularly effective in preventing an end 111 of the current-carrying part 6, which is formed as extending continuously from the electrode 4 formed on the side surface 3 to the upper surface 7 via the edge 101, from being tapered off or broken off.
As an example of the prior art pertaining to the manufacturing method, a method for manufacturing a charging plate disclosed in Japanese Published Unexamined Patent Application No. Hei-9(1997)-314847 (hereinafter referred to as the prior art) is known. The prior art discloses a method for manufacturing a charging plate comprising the following five steps to form electrodes and current-carrying parts on a substrate.
That is, a charging plate is manufactured through a substrate preparation step, a step for forming electrodes made of electrically conductive material on a side surface of the substrate, a step for forming first current-carrying parts connecting ends of the electrodes on an upper surface of the substrate, a step for forming second current-carrying parts made of electrically conductive material on the upper surface of the substrate by bonding the second current-carrying parts to the first current-carrying parts, and a step for coating the upper surface of the substrate with a dielectric material.
In these steps, the electrodes and the first and second current-carrying parts are formed by screen- or stencil-printing and curing an electrically conductive paste. A method for forming the electrodes and the current-carrying parts by exposing the substrate using an electrically conductive photoresist is also disclosed.
The aforementioned charging plates for liquid jet charging device and the methods for making the same have the following problems to be solved.
In the prior art, a charging plate 1C is manufactured by forming a film of electrically conductive material over an area ranging from the side surface 3 to the upper surface 7 of a substrate made of non-conductive material, and then forming a plurality of electrodes 4 and current-carrying parts 5 by etching and other means. This tends to cause the shape of the electrodes 4 formed on the side surface 3 to be collapsed at the distal ends thereof, resulting in irregular distal ends of the electrodes.
As a result, even when each electrode 4 is disposed facing the liquid filament 23 injected through the orifice, the distance between each electrode and the liquid filament 23, which is critical to charge the liquid filament 23, tends to be irregular. Furthermore, because the radius of roundness on the edge 101 of the side surface 3 of the charging plate 1C is closely approximate to the length a of the liquid filament 23, which is approximately 1 millimeter, each electrode 4 cannot be brought adequately close to the liquid filament 23, making the liquid filament 23 injected through the orifice 22 unstable. This leads to some droplets 24 and 24xe2x80x2 produced from the tip of the liquid filament 23 failing to be charged.
In other words, even if attempts are made to bring the charging plate 1C close to the liquid filament 23 injected through the orifice 22, and close to the lower surface of the orifice member 21 so as to bring the electrode 4 provided on the side surface 3 of the charging plate 1C, the edge 101 consisting of the side surface 3 and the upper surface 7 of the charging plate 1C having a roundness with a radius of almost the same size as the length a of the liquid filament 23 prevents the edge 111 of each electrode 4 from being placed adequately close to the liquid filament 23 even if the upper surface 7 of the charging plate 1C is brought as close as almost touching the lower surface of the orifice member 21. Thus, the liquid filament 23 cannot be effectively and invariably charged, and part of the droplets 24 and 24xe2x80x2 produced from the liquid filament 23 fail to be charged.
Next, the charging plate manufactured according to the prior art involves as many as five complicated process steps. This leads to increased manufacturing man-hours and cost.
Furthermore, the manufacturing process according to the prior art is divided into steps for forming electrodes made of conductive material on the side surface of a substrate, forming a first current-carrying part made of conductive material on the upper surface of the substrate, and then forming a second current-carrying part. This tends to cause incomplete electrical connection between the electrodes and the first and second current-carrying parts connected thereto, resulting in imperfect electrical continuity.
Forming current-carrying parts at minute pitches corresponding to a plurality of electrodes formed at minute pitches requires a separate complicate process.
It is a first object of the present invention to solve these problems.
It is a second object of the present invention to form a plurality of electrodes and current-carrying parts with high precision.
It is a further object of the present invention to make it possible bring electrodes formed with high precision close to liquid filaments injected from orifices, thereby charging the liquid filaments instantaneously in an effective and stable state as necessary, so that, droplets produced from the liquid filaments can be reliably charged.
It is a still further object of the present invention to provide a method for manufacturing a charging plate on which current-carrying parts are formed with ease and at low cost.
To accomplish these objectives, the present invention provides a charging plate for liquid jet charging devices in which liquid filaments injected through orifices provided on an orifice member is charged, so that charged droplets are produced by subdividing the liquid filaments, characterized in that
an unrounded edge at which a work surface on an upper surface intersects with one side surface is formed on a substrate made of non-conductive material,
a plurality of electrodes made of conductive material are formed on the one side surface of the substrate, with the distal end thereof aligned with the unrounded edge, at almost equal intervals in the longitudinal direction (in the depth direction in FIG. 8) of the edge,
current-carrying parts made of conductive material individually extending from the electrodes are formed on the lower surface of the substrate, and
the work surface on the upper surface and the side surface of the substrate, both constituting the edge, form an almost right angle or a slightly smaller angle than a right angle.
The present invention also provides a method for manufacturing a charging plate comprising
a first step for forming a film of a conductive material over an area ranging from one side surface to lower surface of a substrate made of non-conductive material,
a second step for forming a plurality of electrodes on one side surface of the substrate and forming current-carrying parts extending from the electrodes on the lower surface of the substrate by partially removing the conductive film, and
a third step for forming a work surface obtained by removing part of the upper surface so that the side surface of the substrate has a predetermined thickness, and causing an edge at which the work surface on the upper surface intersects with the side surface to align with the distal ends of the electrodes.
Furthermore, the second step comprises a corrosion-preventive film forming step for covering with at corrosion-resistant film a portion on which the conductive electrodes and current-carrying parts extending from the electrodes have been formed and an etching step for removing the portion coated with conductive film, excluding the portion coated with corrosion-preventive film, from the substrate.